At present, in an evaluation of characteristics of a driver who drives an automobile vehicle or of drivability of an automobile vehicle, or in performing an operation assist control for assisting an operation performed by a driver who drives an automobile vehicle to thereby control a behavior of the automobile vehicle, information on the automobile vehicle being driven or biological information of the driver who is driving the vehicle are used.
Of those, the drivability of an automobile vehicle is determined based on a balance between two contradictory types of performance such as responsiveness and stability. The responsiveness herein refers to an index for indicating how sensitively the steering state of an automobile vehicle reacts to the operation (for example, steering operation) performed by the driver. When the vehicle is high in responsiveness, the vehicle can be steered greatly even when the driver performs the operation by a significantly light force. Similarly, the stability refers to an index for indicating a degree of insusceptibility of the steering state of an automobile vehicle with respect to an influence due to a disturbance resulting from a road surface irregularity or the like. When the vehicle is high in stability, the vehicle can travel in a stable steering state even when affected by a great disturbance resulting from the road surface irregularity or the like, without the need for a great steering adjustment force to be exerted by the driver driving the vehicle. As has been widely recognized in general, a vehicle which is too high in responsiveness tends to be low in stability, while a vehicle which is too high in stability tends to be low in responsiveness. The drivability of an automobile vehicle, which is determined by the two contradictory types of performance such as the responsiveness and the stability, is difficult to quantify. Conventionally, in order to quantitatively evaluate the drivability of an automobile vehicle, a feeling test has been mainly conducted to make the evaluation. In the feeling test, a driver who drives a vehicle of evaluation target quantitatively evaluates the vehicle of evaluation target in terms of drivability thereof, based on the feeling of the driver oneself.
As regards the feeling test which has been conventionally conducted, Patent Document 1 described below, for example, discloses an apparatus for measuring driving stability of a vehicle, which has been made for the purpose of appropriately evaluating the driving stability of a vehicle based on a quantitative index. Patent Document 1 describes that attention is focused on how the steering operation performed by a driver is affected by external work resulting from a road surface irregularity or the like, and the driving stability is evaluated by using as an index a steering work ratio, which is obtained as a product of a time differential value of a steering angle (steering speed) and a steering force. Patent Document 1 describes that the steering work ratio corresponds to the amount of work externally received due to a road surface irregularity or the like. Further, in particular, in the case where the steering work ratio has a negative value, the wheel steering speed (time differential value of a steering angle) is mutually opposite in direction to the wheel steering force, and accordingly the case is regarded as a state where the driver is trying to stop the movement of the steering wheel and is externally receiving work resulting from a road surface irregularity or the like. In Patent Document 1 described below, the driving stability of a vehicle can be evaluated according to the magnitude of the negative steering work ratio.
Patent Document 1: JP 2002-214083 A